In heat exchangers of the above type, it is common practice where there are height and/or width limitations to increase the heat transfer capacity of a single tube row arrangement by simply adding an additional row of tubes. But this normally adds substantially to the core depth even where the tubes are arranged to overlap since each tube has two legs whose open ends are typically arranged in separate rows to make connection at a header plate with the inlet and outlet chambers in the tank for the two-pass flow by each tube. Moreover, the tank including the header plate must then also be increased in size depthwise to accommodate the additional row of tubes. This can present a substantial limitation particularly where the existing packaging space requirements do not permit the resulting increases in size.
For example, in the use of such a heat exchanger as a heater core in the passenger heating system of an automotive vehicle, the typical heater core with one row of U-shaped tubes may be found to lack sufficient heat capacity in a more demanding application so that an additional row is required. But with two rows of U-shaped tubes, there are normally four rows of tube legs that must be accommodated across the thickness or depth of the core and make connection at the header plate with the inlet and outlet chambers in the tank. However, the resulting increase in core depth even where the tubes are arranged to overlap sideways, may not be possible within the confined space of the existing heater case thereby also requiring accommodating alterations in the latter provided such is possible within its space restraints in the vehicle. Moreover, where the heat exchanger is of the tube and fin type, this requires an accompanying increase in the depth of the fins as well as the tank and header plate.